1. Field
Exemplary embodiments of the present invention relate to semiconductor design technology, and more particularly, to an integrated circuit including a plurality of semiconductor devices which are stacked in a package.
2. Description of the Related Art
In order for a semiconductor device to operate, the semiconductor device generates internal voltages suitable for internal use, using various external voltages. Since the internal voltage is generated using a voltage applied from an external source, it is necessary to monitor whether the generated internal voltage is normal or not.
FIG. 1 illustrates a conventional method for monitoring an internal voltage using a preset pad PAD. FIG. 1 illustrates a case in which a reference voltage VREF is outputted to the pad PAD.
Although “VREF” represents a reference voltage and “VINT” represents an internal voltage used to perform operations in the semiconductor device, both of the voltages are measured in essentially the same fashion.
The monitoring method of FIG. 1 connects a particular internal voltage or reference voltage to the pad PAD and then measures the internal voltage or reference voltage. In this monitoring method, separate control is not required, and the internal voltage or reference voltage is read as it is.
FIG. 2 illustrates a conventional monitoring method using a multi-measuring device. In this method, a controller is provided to select one of a plurality of internal voltages VINT1 to VINT3 and reference voltages VREF1 to VREF3, and a selector is provided to connect the internal voltage or reference voltage selected by the controller to a preset pad PAD.
FIG. 3 illustrates configurations of the controller and the selector which are components of the multi-measuring device of FIG. 2. The controller includes a decoder configured to select a voltage which is to be monitored. The voltage may be one of the internal voltages VINT1 to VINT3 and reference voltages VREF1 to VREF3. For example, when a three-bit select code MON<0:2> is inputted, the controller may selectively monitor up to eight internal voltages.
In this method, when all bits of the select code MON<0:2> are inputted at a low level as an initial value, a default voltage which is one of the plurality of internal voltages VREF1 to VREF3 and VINT1 to VINT3 is connected to the pad PAD. In devices according to FIG. 3, the default voltage is typically the first reference voltage VREF1, but may be changed by a designer. Therefore, during a test operation such as a probe test, the default voltage VREF1 may be connected to the pad PAD to perform a forcing test. That is, in a default state where none of the bits of the select code MON<0:2> are activated to a high level, the default voltage VREF1 for measuring and forcing is connected to the pad PAD.
In a conventional monitoring method, when only one semiconductor device is packaged in an integrated circuit, no problems occur. Instead, since the default voltage VREF1 is connected by default, the forcing test may be implemented easily and quickly. However, when two or more semiconductor devices are packaged in a single integrated circuit, the situation may change.
FIG. 4 illustrates a problem which occurs when a conventional internal voltage multi-measuring device is used to measure internal voltages VREF1 to VREF3 and VINT1 to VINT3 of two or more semiconductor devices stacked in an integrated circuit.
When the internal voltages VREF1 to VREF3 and VINT1 to VINT3 of two or more semiconductor devices in a single package are to be monitored, only the semiconductor device stacked at the lowermost part of the package is directly connected to balls or pins of the packaged integrated circuit. Therefore, input/output pads of the respective semiconductor devices must be connected through a TSV (through silicon via). However, since default voltages are outputted to preset pads of the respective semiconductor devices, the default voltages outputted through the pads may be shorted among the stacked semiconductor devices at the same time when the pads are connected to the same TSV. Furthermore, as described with reference to FIG. 3, the default voltages outputted from the respective semiconductor devices may differ from each other.
For reference, in order to prevent the default voltages from being shorted among the plurality of semiconductor devices having a stack structure as illustrated in FIG. 4, the semiconductor devices may be controlled not to output the default voltages to the pads. In this case, the select code MON<0:2> must be inputted from an external source whenever a semiconductor device is tested, thereby reducing the test efficiency. When several hundred or thousand semiconductor devices must be tested, it may take quite a long time to perform the forcing test using select codes input from an external source.